Abstract

This study introduces two new thermotolerant strains of Kluyveromyces sp. for the biofuel industry to reduce the overall cost of production. The fermentation conditions including temperature, pH, incubation period and sugar concentration were adjusted. The two yeast strains were identified by sequencing of ITS1 and ITS2 regions. Comparing the sequence results with the GenBank reference proved that the strain Kluyveromyces sp. ZMS1 had 100% of similarity with Kluyveromyces maxianus. Yeast strain Kluyveromyces sp. ZMS3 had only 97% of similarity with the reference species; consequently, it could be a new strain. At 35°C, Kluyveromyces sp. ZMS1 GU133329 and Kluyveromyces sp. ZMS3 GU133331 produced 9.55 (w/v) and 11.72% (w/v) of ethanol, respectively. The appropriate concentration of sugar that induced the maximum production of ethanol by these strains was 20 to 25%. The optimum pH range for both strains was 5.0-5.5. In fed-batch culture, the maximum ethanol production was 11.71 (w/v) and 11.62% (w/v) by Kluyveromycessp. ZMS3 GU133331 and Kluyveromyces sp. ZMS1 GU133329, respectively. This study concludes the two thermotolerant yeast strains are promising in the production of bioethanol, especially strain ZMS3 GU133331 that showed a good growth up to 45°C. It grew normally and carried out its fermentation process in 25% of sugar concentration. Application of these new strains will not only decrease the risk of contamination but also reduce in cooling costs that will lead to the reduction of the overall production cost.

Key words:  Bioethanol, Kluyveromyces spp., thermotolerant, ITS, fed-batch.